Field of the Invention
The invention relates to a method and system for establishing a wireless network for audio data transmission between assistive listening devices; in particular, the invention relates to the pairing process required for establishing such network.
Description of Related Art
An assistive listening device is an audio signal transmission unit for transmitting audio signals via the wireless link, such as an RF link, or an audio signal receiver unit for receiving audio signals from another assistive listening device via such wireless link.
One type of wireless network for assistive listening devices such as hearing instruments uses an electromagnetic (i.e., far-field) link for connecting remote accessory devices, such as a wireless microphone, to an ear-level receiver device.
Typically, such remote wireless microphones are used by teachers teaching hearing impaired persons in a classroom (wherein the audio signals captured by the wireless microphone of the teacher are transmitted to a plurality of receiver units worn by the hearing impaired persons listening to the teacher) or in cases where several persons are speaking to a hearing impaired person (for example, in a professional meeting, wherein each speaker is provided with a wireless microphone and with the receiver units of the hearing impaired person receiving audio signals from all wireless microphones). Another example is audio tour guiding, wherein the guide uses a wireless microphone.
Another typical application of assistive listening devices is the case in which, the transmission unit includes a wireless microphone for capturing ambient sound, in particular from a speaker close to the user, and/or a gateway to an external audio device, such as a mobile phone; here the transmission unit usually only serves to supply wireless audio signals to the receiver unit(s) worn by the user.
U.S. Pat. No. 8,019,386 B2 relates to a hearing assistance system comprising a plurality of wireless microphones worn by different speakers and a receiver unit worn at a loop around a listener's neck, with the sound being generated by a headphone connected to the receiver unit, wherein the audio signals are transmitted from the microphones to the receiver unit by using a spread spectrum digital signals. The receiver unit controls the transmission of data, and it also controls the pre-amplification gain level applied in each transmission unit by sending respective control signals via the wireless link.
International Patent Application Publication WO 2008/098590 A1 relates to a hearing assistance system comprising a transmission unit having at least two spaced apart microphones, wherein a separate audio signal channel is dedicated to each microphone, and wherein at least one of the two receiver units worn by the user at the two ears is able to receive both channels and to perform audio signal processing at ear level, such as acoustic beam forming, by taking into account both channels.
One option to implement a wireless network for hearing instruments is to use a time division multiple access (TDMA) scheme with central or distributed network management, wherein one of the devices acts as a master and determines the time slots during which each network device may transmit data and communicates this transmission schedule to the participating devices. A device entering the network must first register with the network master and can subsequently request reservation of time slots to transmit its data to recipient devices, i.e., a device is allowed to transmit only once it has synchronized with the network. In case that the network uses a frequency hopping scheme, the master transmits the necessary information to the synchronized devices.
An example of a wireless network for hearing devices is described in U.S. Pat. No. 8,150,057 B2, wherein audio signals are transmitted from a plurality of wireless microphones worn by various speakers via the wireless network to a receiver unit worn by a listener. Each of the transmission devices has certain dedicated slots in the TDMA scheme for transmitting the audio signals captured by the microphone to the receiver unit.
Another example of a wireless network suitable for audio signal transmission is the Bluetooth standard.
U.S. Pat. No. 8,194,902 B2 relates to a wireless network comprising a binaural hearing aid and other components, like a mobile phone, wherein a TDMA structure is used in a frequency hopping scheme, and wherein, during acquisition/synchronization, the frequency hopping scheme has a reduced number of frequency channels and the new device activates its receiver at a rate different from the frame rate of the network until synchronization data is received from the master device, whereupon the frame timing of the new device is synchronized to the frame timing of the network.
In general, establishing a private communication network requires two steps: first, the devices have to be paired and then the devices have to be synchronized. The pairing procedure typically involves the exchange of the network ID and the network rules (i.e., rules concerning which device is allowed to communicate in which way with whom); the synchronization procedure involves the exchange of information concerning network protocol and timing (i.e., in order to synchronize to a “network clock”), frequency hopping sequence, etc.
In general, pairing may require user action, may occur automatically or may be done already at the manufacturer. For example, pairing between a Bluetooth headset and a mobile phone may require user action, whereas pairing between a computer mouse and a wireless dongle typically is done at the manufacturer. Typical issues concerning the pairing procedure are reliability (i.e., to ensure that pairing with the target device is successful), selectivity (i.e., to avoid inadvertent pairing with unwanted devices), intrusion avoidance (to avoid that an unwanted person is able to pair one of his devices), and privacy (to avoid unwanted persons to sniff pairing and become part of the network).
Whereas reliability can be achieved relatively easily by using a correctly budgeted inductive or RF link, various approaches are known in the art to contribute to selectivity, intrusion avoidance and privacy: pairing may be restricted in time by enabling pairing only during given time windows; such time window may be started, for example, by pressing a button or after power-up of the device. Shorter time windows enhance protection but make the system more difficult to handle. Pairing may be restricted in space, so that pairing is possible only if both devices are within a given range; for example, use of an inductive link inherently results in a severe range restriction. Pairing may be restricted by requiring certain user actions in order to confirm and permit pairing, such as by typing a PIN code on both devices, reading and verifying a PIN code, pressing an OK button, etc.
U.S. Pat. No. 8,554,140 B2 relates to an automatic pairing procedure for audio signal transmission/reception devices, such as a wireless microphone, a music player, a PC or an audio extension device of a TV set, wherein the range of pairing is adjustable by control of the transmission power; it is mentioned that the maximum allowable pairing distance may be set from 0.05 m to 0.5 m.
U.S. Pat. No. 8,300,864 B2 relates to an inductive digital link between a hearing system and a telephone apparatus, wherein the same link is used not only for pairing but also for audio data transmission. Pairing occurs automatically.
International Patent Application Publication WO 2010/1084921 A1 relates to an inductive near field audio data link between a mobile phone and a hearing aid, wherein the near field link is also used for pairing, with pairing occurring automatically.
U.S. Pat. No. 8,650,613 B2 relates to an automatic pairing procedure between Bluetooth devices.
U.S. Pat. No. 7,813,762 B2 and U.S. Pat. No. 8,027,638 B2 relate to a pairing procedure of an ear level audio receiver with a remote Bluetooth device, wherein the receiver may be provided with one or more push buttons by which pairing is facilitated.
International Patent Application Publication WO 2012/056298 A2 relates to pairing of the external part of a cochlea implant system to a remote device, wherein a RF far field link and a near field link are involved in parallel. The RF link is used for the desired communication with the remote device, whereas both the near field and RF link are used for pairing. An “initiate pair” command and a “confirm pairing” command are transmitted via the near field link, and a “pair” command and an “accept” command are transmitted via the RF link. It is mentioned that the devices could be configured such that either one or both of the devices may request pairing by a single button press.